This invention relates to methods for inhibition of inflammatory disease, in particular the inhibition of genetic expression which leads to the reduction or elimination of immune cell proliferation in inflammation or pre-inflammatory conditions.
Inflammation is a tissue reaction to irritation, infection or injury marked by localized heat, swelling, redness, pain and sometimes loss of function. When tissues sustain physiological injury, the afflicted cells synthesize and/or release chemicals (cytokines and cellular adhesion molecules) which attract lymphoid cells and accelerate cell growth which is required for healing. The infiltration of lymphoid cells to the wound leads to the release of more biological response modifying molecules, which include vasoregulatory substances such as bradykinin and immunoregulatory molecules exemplified by the interleukin family of proteins. As healing occurs, the immune cell infiltration wanes and the inflammatory process ceases. Under certain physiological conditions, such as those observed in psoriasis, asthma, head injuries and systemic inflammatory response syndrome (SIRS), the condition persists because of inappropriate cellular controls. A persistent inflammatory condition may be acute or chronic and is generically referred to as inflammatory disease.
Inflammatory disease is exemplified by psoriasis, which is a skin disease caused by excessive growth of basal keratinocytes in the epidermis. It is believed that this uncontrolled growth of the keratinocytes results from stimulation by infiltrating T-cells. The conversion of normal skin to a psoriatic lesion is initiated by injury to the tissue and subsequent recognition of the injury by circulating immune cells. An acute inflammatory reaction ensues and results in the release of various cytokines and growth factors, including tumor necrosis factor alpha (TNF-.alpha.) and interleukin-1 (IL-1). A number of the cytokines released by infiltrating leukocytes induce production of cell adhesion molecules on the surface of the keratinocytes, while others induce the proliferation of basal keratinocytes and result in the release of keratinocyte factors which either auto-stimulate further growth or inhibit normal controls which limit keratinocyte proliferation. The injury further results in the local activation of T-cells which return to the circulation and may cause subsequent psoriatic conditions which are quite distant from the original site of injury.
Induction of the acute phase inflammatory reactants results in the production of IL-1 and TNF-alpha; both of these molecules induce the appearance of the T-cell homing proteins, I-CAM, ELAM-1 and VCAM-1 on the cell surface of keratinocytes. TNF-.alpha. also induces the production of TGF-.alpha., IL-6 and IL-8 by the keratinocytes. The cytokines and growth factors produced by the keratinocytes and infiltrating leukocytes cause uncontrolled keratinocyte proliferation. As the basal layer keratinocytes proliferate, the suprabasal keratinocytes are pushed closer to the surface of the skin where they normally form the cornified envelope layer and the stratum corneum. The abnormal rate of proliferation by the basal keratinocytes results in improper formation of the epidermis and stratum corneum and the ultimate development of the red, scaly appearance which is characteristic of psoriatic skin. The lack of keratinocyte growth regulation has been attributed to an unidentified mutation in a single gene or group of genes in which the keratinocytes no longer respond to the termination signal for wound healing.
There are 3 million patients in the United States afflicted with psoriasis. The available treatments for psoriasis are corticosteroids. The most widely prescribed are TEMOVATE (clobetasol propionate), LIDEX (fluocinonide), DIPROLENE (betamethasone propionate), PSORCON (diflorasone diacetate) and TRIAMCINOLONE formulated for topical application. The mechanism of action of corticosteroids is multifactorial and probably not due to simple inhibition of cell replication. This is a palliative therapy because the underlying cause of the disease remains, and upon discontinuation of the treatment the disease returns. Discontinuation of treatment is often prompted by the appearance of adverse effects such as atrophy, telangiectasias and purpura. Corticosteroids are not recommended for prolonged treatments or when treatment of large and/or inflamed areas is required. Alternative treatments include retinoids, such as etretinate, which has been approved for treatment of severe, refractory psoriasis. Alternative retinoid-based treatments are in advanced clinical trials. Retinoids act by converting keratinocytes to a differentiated state and restoration of normal skin development. Immunosuppressive drugs such as cyclosporine are also in the advanced stages of clinical trials. Due to the nonspecific mechanism of action of corticosteroids, retinoids and immunosuppressives, all current treatments of psoriasis exhibit severe side effects and should not be used for extended periods of time unless the condition is life-threatening or disabling. There is a need for a less toxic, effective therapeutic agent in psoriatic patients.
Asthma affects nearly 5% of the population in industrialized nations, yet it is underdiagnosed and undertreated. There is evidence that the incidence and prevalence of asthma are rising. These trends are occurring despite increases in the available therapies for asthma, which suggests that current methods of treating asthma are inadequate or not being utilized appropriately. Recently, it has been recognized that chronic asthma involves a characteristic inflammatory response in the airways.
Although it has long been acknowledged that fatal asthma is associated with inflammatory changes in the submucosal surfaces of the airways, it is now apparent that inflammation is present in patients with very mild asthma. Biopsies of patients have shown that infiltration of immune cells, especially eosinophils and lymphocytes, and epithelial shedding are prominent features. Further, there is a strong correlation between the degree of eosinophilia and the degree of bronchial hyperresponsiveness. Eosinophils are localized to areas of epithelial damage in the airways of patients. The basic proteins released by the eosinophils may be responsible for the damage observed in these patients. The role of mast cells and neutrophils in the disease is uncertain. Lymphocytes are present at the sites of tissue damage, but their role may be as mediators to amplify the eosinophilic response. In fact, interleukin-5, which is released by T-lymphocytes, is important in retaining and priming eosinophil action in the airway.